Hydraulic operating system



1962 u. R. TOGNELLA 3,050,079

HYDRAULIC OPERATING SYSTEM Filed March '10, 1960 Inventor: U 8 o R.Tog'nel la,

b9 fr-M Attor n e g.

United rates This invention relates to a hydraulic operating system thatutilizes a pneumo-hydraulic accumulator as a source of energy and, moreparticularly, relates to means for providing a reliable indication ofthe amount of energy stored within the accumulator.

The usual pneumo-hydraulic accumulator comprises a pressure vesselcontaining a volume of gas that is compressed by pressurized liquidpumped into the pressure vessel. This compressed gas acts as a source ofstored energy that forces pressurized liquid from the accumulator whenthe liquid is released. In my hydraulic operating system, release of theliquid is effected by means of a suitable controlling valve connected ina hydraulic line communicating with the pressurized liquid. Opening ofthis controlling valve allows the compressed gas in the accumulator toexpand and force pressurized fluid through the line to perform a desiredcontrolling operation.

In certain applications of hydraulic operating systems of this generaltype, it is of extreme importance that no attempt be made to perform thedesired controlling operation if insufficient energy is available fromthe accumulator to complete the operation. For example, if the hydraulicsystem is being used for closing an electric circuit breaker against afaulted power line, insuflicient available energy could result installing of thebreaker in a partially closed position with possibleserious damage to the breaker and connected apparatus resulting.

In such applications, it is therefore important that there be availablesome external indication of the amount of energy stored in theaccumulator. It has heretofore been diflicult to obtain such an externalindication of the available energy primarily because in a conventionalaccumulator, pressure alone is not a reliable indication of thisquantity. The difficulty with the usual system that relies simply upon ameasurement of accumulator pressure is that it is not sensitive toleakage of gas from the accumulator. True, so long as no leakage hasoccurred, pressure alone is a reliable indication of available energy,but once leakage has begun to occur this reliability is lost. In thisregard, the pump that is used for charging the conventional accumulatoroperates to maintain the pressure therein at a desired levelirrespective of the amount of gas that is present. Even after leakagehas reduced the amount of gas to an unacceptably low value, the pressurewithin the accumulator would still be at its normally high level due tothe compensating action of the liquid pump.

Numerous proposals have been made for rendering such systems sensitiveto a loss of gas from the accumulator, but these have usually involvedundue complications. For example, it has been proposed to extend a rodfrom the piston through one end of the accumulator to provide anindication of piston position. This approach is disadvantageous in thatit requires a seal about the rod which can be an added source ofleakage. It has also been proposed to use electrical limit switchesmounted inside the accumulator to provide an indication of pistonposition, but this is disadvantageous in that it requires high pressurelead-throughs for the wires leading to the limit switch. It has beenfurther proposed to use an electronic piston position indicator, butsuch indicators are relatively complicated and expensive and can be asource of trouble.

Accordingly, an object of my invention is to provide,

" atent O 3,050,079 Patented Aug. 21, 1962 in a hydraulic controllingsystem of this general type, simple, inexpensive, and reliable meanssensitive to a loss of gas from the hydraulic accumulator for providingan indication of the amount of energy stored within the accumulator.

Another object is to provide energy-detecting means of this nature whichcan warn that a gas leak is present before the leak has rendered thehydraulic system unsafe or unsuitable for further operations.

Another object is to construct this energy-detecting means in such amanner that it is not susceptible to false operation as a result ofnormal operations of the hydraulic system.

In carrying out my invention in one form, I provide a hydraulicoperating system that includes a pneumohydraulic accumulator comprisinga cylinder and a piston movably mounted within the cylinder to dividethe cylinder into a liquid chamber and a gas chamber at the respectiveopposite sides of the piston. The accumulator is charged by suitablepumping means that acts to force liquid into the liquid chamber.Operation of the pumping means is terminated when the pressure of theliquid exceeds a first predetermined value. A stop within the cylinderlimits the travel of the piston in a direction to compress any gaswithin the gas chamber. The gas chamber normally contains sufiicient gasto maintain the piston spaced from the stop when the pressure of theliquid equals this first predetermined value. So long as no gas leak ispresent in the accumulator, the piston will remain spaced from the stop,and the pressures on its opposite sides will be substantially equal. Ifa gas leak should occur, however, the pressurized liquid will eventuallydrive the piston into engagement with the stop, whereupon further gasleakage will produce a pressure differential on opposite sides of thepiston. This pressure dilferential, and hence a gas leak, is sensed bydifferential pressure means which is sensitive to pressure diflerentialson opposite sides of the piston.

For a better understanding of my invention, reference may be had to theaccompanying sheet of drawing, wherem:

The single figure is a schematic view of a hydraulic operating systemembodying one form of my invention. The system is shown in a chargedcondition.

Referring now to the drawing, there is shown a fluid motor 8 that isarranged to operate a suitable utilization device shown in block form at9. The energy for operating the motor is derived from a pneumo-hydraulicaccumulator 10 which comprises a cylindrical pressure vessel 12 and apiston 14 slidably mounted for vertical movement in the bore of thecylindrical pressure vessel 12.

The piston 14 divides the cylinder 12 into a gas chamber 18 on the upperside of the piston and a liquid chamber 20 on the lower side of thepiston. A suitable seal 21 provided about the outer periphery of thepiston 14 prevents fluid 'from either of these chambers from leakingaround the piston and assures that there will be no direct communicationbetween these fluids. The gas chamber 20 is closed ofl at its upper endduring normal operation of the accumulator 10 but is provided with ahigh pressure supply line 22 through which gas can be supplied to thegas chamber 18 to precharge the accumulator to the desired extent. Oncethe desired amount of gas has been supplied to the gas chamber 18, thesupply line 22. is closed by means of a suitable valve 23.

Communicating with the liquid chamber 20 beneath the piston 14 is ahydraulic line 24 located at the lower end of the accumulator. Liquid isforced through this line 2-4 into the liquid chamber 20 by means of asuitable source of pressure such as pump 26. This pump 26 is operated bymeans of a suitable electric motor 27 that is controlled by aconventional pressure sensitive switch schematically shown at 28. Thecontrolling portion of the pressure sensitive switch 28 communicateswith the liquid chamber 20 and is sensitive to the pressure therein.When the pressure in liquid chamber 20 falls below a predeterminedminimum value, the switch 28 closes its contacts 30 to complete anenergizing circuit 31 for the motor 27. The motor responds by operatingthe pump 26, thereby causing the pump to force liquid into theaccumulator through the line 24. This pumping action continues until apredetermined maximum pressure is reached, whereupon the pressuresensitive switch 28 responds by opening its contacts 30 to interrupt theen ergizing circuit 31 for the motor, thereby terminating pump operationwhen this maximum pressure is reached. In the drawing, the system isdepicted just after the pressure responsive switch 28 has opened toterminate pumping action.

The pump 26, in forcing liquid into the liquid chamber 20, forces thepiston 14 upwardly to compress the gas in chamber 18, thereby storingenergy in this gas for subsequent utilization, as will soon appear. Astop 32 is interposed in the path of movement of the piston to limit itsupward travel under certain abnormal conditions, which will soon bedescribed, but normally there is sufficient gas present within the gaschamber 18 to prevent the piston 14 from reaching stop '32. In otherWords, under normal conditions, the previously-mentioned maximumpressure is reached before the piston 14 has reached the stop 32, and,thus, the pressure sensitive switch 28 terminates operation of the pump26 while the piston 14 is still spaced from the stop 32.

For controlling the release of energy from the accumulator 10, acontrolling valve 34 is interposed in the line 24 between theaccumulator 1t) and the motor 8. This valve 34 is normally closed andthus normally prevents any pressurized liquid from flowing from theaccumulator to the motor 8. When the valve 34 is operated to openposition, the compressed gas above the piston 14 is free to expand and,in so doing, forces the piston 14 downwardly, driving pressurized liquidthrough the thenopen valve 34 into the cylinder 40' of the motor. Thepressurized liquid entering the cylinder 40 drives the piston 42 of themotor downward to produce the desired operation of device 9. When thepiston 42 of the motor has completed its downward operating stroke, thevalve 34 is returned to its closed position to block the further flow ofliquid from the accumulator to the motor 8. Preferably, the valve 34 isa three-way valve that vents the motor 8 to a low pressure sump whenvalve 34 is returned to its closed position. A suitable valve of thisnature is shown and claimed in application Serial No. 856,122,Coggeshall et al., filed November 30', 1959, now Patent No. 2,972,337,and assigned to the assignee of the present invention.

In the disclosed operating system, the valve 34 is electricallycontrolled by means of a suitable solenoid 46, which is connected in anenergizing circuit 48. This energizing circuit 48 also includes amanually-controlled operation-initiating switch 49, a limit switch 50,and the normally-closed contacts 52 of a pressure sensitive interlockswitch 54, all connected in series with each other and the solenoid 46.

Assuming that the limit switch 50 and the contacts 52 of the pressuresensitive switch 54 are closed, operation of the solenoid 46 can beeffected simply by closing the switch 49 to complete the energizingcircuit 48 for the solenoid. When the piston 42 of the motor hascompleted its working stroke in response to energization of solenoid 46,the energizing circuit 48 is opened by the limit switch 50, thus causingthe valve 34 to return to its closed position. When the motor piston 42is returned at least partially to its position shown in the drawing, thelimit switch 50 is reclosed and the circuit 48 is again prepared foranother operation. Any suitable conven tional means may be used forcontrolling the limit switch in this manner. The pressure sensitiveportion of interlock switch 54 is connected to the gas chamber above thepiston 14 of the accumulator 10 and is arranged to open its contacts 52when the gas pressure falls below a predetermined minimum value. In apreferred form of my invention, this minimum value is a pressureslightly above the minimum pressure capable of producing a completeoperation of the motor piston 42 if the accumulator piston 14 wasresting against the stop 32 when the valve 34 was opened. Thus, theswitch 54 opens to block operation of the valve 34 whenever insufiicientgas pressure is present within the accumulator to assure successfulcompletion of the desired controlling operation.

"the stop 32 performs the highly desirable function of rendering thepressure responsive device 54 sensitive to the leakage of gas from theaccumulator. Without the stop 32, gas could leak from the accumulator 10without any significant effect on the pressure to which the device 54 isexposed. This would be the case because the pump 26 would maintain thepressure within the accumulator 10 above the minimum pressure setting ofswitch 54 despite any gas leakage. The pump would simply forceadditional liquid into the accumulator to compensate for the loss of gasthrough leakage. With the stop 32 present, however, the pump 26 canforce liquid into the accumulator only until the piston 14 encountersthe stop. Thereafter, any gas leakage that occurs will not becompensated for by the pump and will reflect itself in falling gaspressure. When this gas pressure has finally fallen to a level that istoo low to assure successful operation of the device 9 by the motor 8,the pressure sensitive switch 54 will open its contacts 52 and preventthe controlling valve 34 from being opened to initiate operation of themotor 8.

The pressure setting of the pressure responsive switch 54 issufficiently low to prevent the switch 54 from opening its contacts todisable the valve 34 in response to the pressure drops resulting fromone or even several normal operations of the motor 8. For example,accumulator 18 of the disclosed system is designed so that it hassufficient capacity to provide for six closely-successive operations ofthe motor B. Five such operations would substantially lower the gaspressure in the accumulator 10, but if the accumulator were initiallyfully charged, these five operations would not lower the pressuresufiiciently to open the pressure responsive switch 54. A closelysuccessive sixth operation would result in opening of the switch 54, butthis sixth operation could take place without hindrance from thepressure-responsive switch 54. Thus, it will be apparent that thepressure within the accumulator is normally maintained at pressuresconsiderably higher than the setting of switch 54 to provide for aseries of closely successive normal operations.

Since the switch 54 is insensitive to normal pressure drops within theaccumulator, it cannot warn of a loss of gas from the accumulator 10until the loss has reduced the gas pressure to a value substantiallybelow the normally-occurring minimum pressure. By this time, the gaspressure might be too low to assure successful operation of the motor 8,and the operator would then have had no opportunity to prepare for thissituation, even though the leak might have first begun days or evenweeks earlier.

It is therefore desirable that some warning be given of a gas leak wellahead of the time that the leak renders the system inoperative throughopening of the pressure sensitive switch 54. For providing this earlyWarning, I provide a conventional differential pressure switch 60 whichis sensitive to a difference in pressure on opposite sides of the piston14. This differential pressure switch 60 is schematically depicted ascomprising a pair of pressure sensitive bellows 60a and 60b, one 60aconnected to the gas chamber 18 of the accumulator through a line 62 andthe other 6011 connected to the liquid chamber 20 of the accumulatorthrough a line 64. Contacts 61a and 61b are respectively carried at thelower, or movable, ends of these bellows 60a and 60b. So long as theliquid and gas pressures are equal the contacts remain spaced apart, butif the liquid pressure should exceed the gas pressure by a predeterminedamount, the contact 61b will overtake the contact 61a and thus completean alarm circuit 65, energizing and sounding a suitable alarm Aconnected in this circuit 65. The switch 60 is so adjusted that thepressure differential required to effect this operation is considerablyless than the difference between the opening setting of thepressureresponsive switch 28 and the opening setting ofpressureresponsive switch 54. For reasons which will soon be apparent,operation of the differential pressure switch 60 is indicative of a gasleak in the accumulator. Sounding of the alarm A thus informs thestation attendant that a gas leak is present and that appropriatepreparations and steps should be taken for its correction.

This gas leak might very well be a slow one which would not impair theability of the accumulator to produce a successful operation of themotor for days or even weeks, and it would therefore be premature atthis time to render the motor 8 inoperative through opening of theswitch 54. Since the switch 54 remains closed until there isinsufiicient accumulator pressure to assure completion of a motoroperation, it will be apparent that the attendant is not precluded frominitiating any opera tion that the accumulator is then capable ofcarrying through to completion, even though a gas leak is present.

The differential pressure switch 60 will remain inactive, or open, solong as the accumulator piston 14 is spaced from the stop 32 inasmuch asthe pressures on opposite sides of the piston 14 will be equal underthese circumstances. It is only when the piston 14 reaches the stop 32that a pressure differential can build up on opposite sides of thepiston 14. The pressure responsive switch 28 that controls the pump 26is so adjusted that if no gas leak is present, the piston 14 will remainspaced from the stop 32 inasmuch as the pressure in the accumulator willnormally be sufficiently high to open the switch 28 and terminatepumping prior to the pistons reaching the stop 32. Only when a gas leakis present, will the pump 26 be capable of forcing the piston 14 intoengagement with the stop 32 before the switch 28 opens to terminatepumping action. In summary, the establishment of a pressure differentialon opposite sides of the piston 14 indicates that the piston has engagedstop 32, and the pistons engaging stop 32 indicates that a gas leak ispresent.

Because the pressure differential switch 60 operates in response to amuch smaller differential in pressure than the difference in thesettings of total pressure switches 28 and 54, the switch 60 can respondmuch more quickly to the presence of a gas leak than can the pressureresponsive switch 54, thus providing the desired early warning of thegas leak.

As examples of the pressure settings of the various switches, in onetypical embodiment of my invention the pump-controlling switch 28 isarranged to close its contacts whenever the liquid pressure falls below2950 p.s.i. and to open on rising pressure whenever the liquid pressurereaches 3000 p.s.i. The gas pressure switch 54 is arranged to open onfalling pressure Whenever the gas pressure falls below 2500 p.s.i. andto close on rising pressure at about 2550 p.s.i. The pressuredifferential switch 60 is arranged to close whenever the pressuredifferential exceeds about 100 p.s.i. There is thus a 500 p.s.i.difference between the opening settings of switches 28 and 54 ascompared to the 100 p.s.i. value for which the differential pressureswitch is set. Accordingly, a 100 6 p.s.i. pressure differential soundsthe alarm A, but a 500 p.s.i. differential is normally required to causethe switch 54 to disable the controlling valve 34.

It is to be noted that the pump-controlling pressure switch 28 islocated in communication with the liquid chamber 20 instead of with thegas chamber 18 of the accumulator. This location of the pressure switch28 is advantageous in that it assures that the pumping action will beterminated whenever the liquid pressure reaches a desired maximum value.If the switch 28 were located in communication with gas chamber 18instead of liquid chamber 20, it would be insensitive to liquid pressureafter the piston encountered stop 32 and would allow the pump to raisethe liquid pressure to an undesirably high level.

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from myinvention in its broader aspects, and I, therefore, intend in theappended claims to cover all such changes and modifications as fallwithin the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a hydraulic operating system, a pneumo-hydraulic accumulatorcomprising a cylinder and a piston mov ably mounted within said cylinderto divide the cylinder into a liquid chamber and a gas chamber at therespective opposite sides of said piston, means including a source ofpressure connected to said liquid chamber and operable to force liquidinto said liquid chamber, pres sure responsive means operativelyconnected to said cylinder for effectively terminating operation of saidsource of pressure when the pressure of the liquid in said liquidchamber exceeds a first predetermined value, a stop arranged within saidcylinder for limiting the travel of said piston in a direction tocompress any gas within said gas chamber, said gas chamber normallycontaining suflicient gas at a sufficient pressure to maintain saidpiston spaced from said stop when the pressure of said liquid equalssaid first predetermined value, differential pressure responsive meansoperatively connected to said liquid and gas chambers and sensitive to apressure differential between the gas and the liquid on opposite sidesof said piston for providing a controlling signal when said pressuredifferential exceeds a predetermined amount.

2. In a hydraulic operating system for effecting predeterminedcontrolling operations, a pneumo-hydraulic accumulator comprising acylinder and a piston movably mounted within said cylinder to divide thecylinder into a liquid chamber and a gas chamber at the respectiveopposite sides of said piston, means including a source of pressureconnected to said liquid chamber and operable to force liquid into saidliquid chamber, pressure responsive means connected to said cylinder foreffectively terminating operation of said source of pressure when thepressure of the liquid in the liquid chamber exceeds a firstpredetermined value, a stop arranged within said cylinder for limitingthe travel of said piston in a a direction to compress any gas withinsaid gas chamber, said gas chamber normally containing sufiicient gas ata suflicient pressure to maintain said piston spaced from said stop whenthe pressure of said liquid equals said first predetermined value, acontrolling valve operatively connected to said liquid chamber forreleasing liquid from said accumulator to effect said predeterminedcontrolling operations, differential pressure responsive means connectedto said liquid chamber and said gas chamber and sensitive to a pressuredifferential between the gas and the liquid on opposite sides of saidpiston for providing a controlling signal when said differential exceedsa predetermined amount, means operatively connected to said gas chamberfor rendering said controlling valve incapable of releasing liquid fromsaid accumulator when the pressure in said gas chamber is below a secondpredetermined value substantially less than said first predeterminedvalue, said differential pressure responsive means operating in responseto a substantially smaller pressure differential than the differencebetween said first and said second predetermined pressure values so asto provide an early warning of the loss of gas firom said accumu-lator.

3. In a hydraulic operating system for eifecting predeterminedcontrolling operations, a pneumo-hydrtaulic accumulator comprising acylinder and a piston movabiy mounted within said cylinder to divide thecylinder into a liquid chamber and a gas chamber at the respectiveopposite sides of said piston, means including a source of pressureconnected to said liquid chamber and operable to force liquid into saidliquid chamber, pressure responsive means operatively connected to saidcylinder for effectively terminating operation of said source ofpressure when the pressure of the liquid in said liquid chamber exceedsa first predetermined value, a stop arranged Within said cylinder forlimiting the travel of said piston in a direction to compress any gaswithin said gas chamber, said gas chamber normally containing sufficientgas at a suflicient pressure to maintain said piston spaced from saidstop when the pressure of said liquid equals said first predeterminedvalue, a controlling valve operatively connected to said liquid chamberfor releasing liquid from said accumulator to effect said predeterminedcontrolling operations, said accumulator having suflicient capacity toprovide the energy for a series of said controlling operations occurringin close succession, means operatively connected to said gas chamber andresponsive to a drop in the pressure in said gas chamber to a levelbelow a second predetermined value for rendering said controlling valveincapable of releasing liquid from said accumulator, said secondpredetermined value being below the lowest value of pressure thatresults from two closely successive normal controlling operations ofsaid system initiated when the liquid pressure is at least as high assaid first predetermined value.

4. In a hydraulic operating system for effecting predeterminedcontrolling operations, a pneumo-hydraulic accumulator comprising acylinder and a piston movably mounted within said cylinder to divide thecylinder into a liquid chamber and a gas chamber at the respectiveopposite sides of said piston, means including a source of pressureconnected to said liquid chamber and operable to force liquid into saidliquid chamber, pressure responsive means operatively connected to saidcylinder for efiectively terminating operation of said source ofpressure when the pressure of the liquid exceeds a first predeterminedvalue, a stop arranged within said cylinder for limiting the travel ofsaid piston in a direction to compress any gas Within said gas chamber,said gas chamber normally containing suflicien-t gas at a sufiicientpressure to maintain said piston spaced from said stop when the pressureof said liquid equals said first predetermined value, said accumulatorhaving sufficient capacity to provide the energy for a series of saidcontrolling operations occurring in close succession, means operativelyconnected to said gas chamber and responsive to a drop in the pressurein said gas chamber to a level below a second predetermined value forproviding a controlling signal indicating a gas leak from said gaschamber, said second predetermined value being below the lowest value ofpressure that results from one normal controlling operation of saidsystem initiated when the liquid pressure is at least as high as saidfirst predetermined pressure.

5. A hydraulic operating system of claim 4- in combination withdifferential pressure responsive means operatively connected to saidliquid chamber and said gas chamber and sensitive to a pressuredifierential between the gas and the liquid on opposite sides of saidpiston for providing a controlling signal when said d-ifiercntialexceeds a. predetermined value, said differential pressure responsivemeans operating in response to a substantially smaller pressuredifferential than the difierence between said first and said secondpredetermined pressure values so as to provide an early warning of aloss of gas from said accumulator.

6. The hydraulic operating system of claim 1 in which said pressureresponsive means for terminating operation of said source of pressuremeans comprises a pressure sensitive switch having a controlling portioncommunicating with the liquid chamber of said accumulator.

References Cited in the file of this patent UNITED STATES PATENTS1,915,576 Mullen June 27, 1933 1,938,956 Fee Dec. 12, 1933 2,244,392Em'anueli June 3, 1941 2,621,608 McIntyre Dec. 16, 1952 2,734,960Reynolds Feb. 14, 1956 2,956,581 Pearson Oct. 18, 1960

